Planned wedge size compared to achieved advancement in dogs undergoing the modified Maquet procedure.

OBJECTIVES: To evaluate the patellar ligament to tibial plateau angle (PL-TPA) and amount of achieved advancement in dogs that underwent the modified Maquet procedure; compare wedge sizes recommended using two different planning techniques (Orthomed and modified tibial tuberosity advancement); and evaluate anatomical factors that predict the wedge size required to obtain a 90° PL-TPA. METHODS: Pre- and postoperative radiographs of dogs that had a modified Maquet procedure performed were evaluated for the following: calculated wedge size using two different planning techniques, the actual wedge size used, the achieved tibial tuberosity advancement, and the changes in PL-TPA. Anatomical measurements of the tibia were evaluated and correlated with the actual wedge size. RESULTS: Of the 38 modified Maquet procedures identified, 53% (n = 20) had a PL-TPA of 90° ± 5°. Actual achieved advancement of the tibial tuberosity was 30% less than the wedge size used. Changes in PL-TPA and tibial width persisted at eight weeks postoperatively without loss of advancement. The two planning techniques did not result in a significantly different selection of wedge size. CLINICAL RELEVANCE: Current planning techniques for the modified Maquet procedure result in under-advancement of the tibial tuberosity. Both measurement techniques evaluated do not result in appropriate advancement.

Variability associated with assessing changes in position of a canine uncemented femoral stem prosthesis.

OBJECTIVE: Evaluate variability associated with assessing changes in the position of uncemented femoral stems. METHODS: Stem level, canal fill, stem angle, and version angle were measured on craniocaudal horizontal beam (CCHB) and open leg lateral (OLL) radiographic projections of the femur of 20 dogs that had uncemented total hip replacement. Intraobserver and interobserver repeatability were determined on immediate postoperative (PO) images. Differences in position were calculated between the first (3 months - R1) and second (6 months - R2) re-evaluation (R1-R2) time points, and between PO and R1. RESULTS: The measurement process was very repeatable. For R1-R2, the stem appeared to subside 0.8 ± 1.4 mm for measurements based on the greater trochanter on the CCHB images, but there was a wide range (-3.9 to 2 mm; positive values indicate proximad movement). Measurements based on the intertrochanteric crest on the OLL images had the same mean, and also a wide range (-4.4 to 2.1 mm; negative values indicate proximad movement). For PO-R1, the stem appeared to subside 1.8 ± 2.0 mm (CCHB, based on the greater trochanter, range -7.7 to 2.2 mm), 1.6 ± 1.5 mm (CCHB, based on the intertrochanteric crest, range -0.7 to 4.3 mm); and 2.1 ± 2.1 mm (OLL, based on the intertrochanteric crest, range -1.6 to 6.8 mm). CONCLUSION: The position of a stable stem can appear different on subsequent re-evaluations, but this may be due to variability associated with inconsistency of positioning of the patient and limb. CLINICAL SIGNIFICANCE: Documenting subsidence in individual patients should not rely on calculations based on a single measurement.

Acetabular cup liner and prosthetic head exchange to increase the head diameter for management of recurrent luxation of a prosthetic hip in two dogs.

Component malalignment and impingement are possible causes of recurrent luxation following total hip replacement in the dog. In the two cases presented in this report, luxation that was probably due to impingement was managed by exchanging the standard 17 mm prosthetic head for a 24 mm prosthetic head. This required removal of the original acetabular cup liner and placement of a new polyethylene liner that would accept the 24 mm head into the stable acetabular shell. In the first case, a 50 kg Malamute dog, recurrent luxation was initially managed by component alignment revision, iliofemoral suture, triple pelvic osteotomy and a novel lasso technique, without long-term success. After exchanging the head and cup liner, luxation did not recur over a 12-month period. In the second case, a 65 kg Newfoundland dog, impingement was suspected after a second luxation event. Luxation did not recur during the nine months after exchange of the head and cup liner. The larger prosthetic head used in these two cases increased the impingement-free range-of-motion of the joint and increased the translation distance required for luxation (jump distance).

Revision of a loose cementless short-stem threaded femoral component using a standard cementless stem in a canine hip arthroplasty.

A Helica short-stemmed femoral prosthesis that was identified as being loose one year after implantation was revised with a standard long stem cementless BFX femoral prosthesis. A double pelvic osteotomy was also performed to improve the orientation of the stable acetabular cup. Despite complete resorption of the femoral neck, and a large perforation of the lateral femoral cortex, the revision stem did not subside or rotate. The prosthetic joint did not dislocate. At re-evaluation two years after revision surgery, the prosthetic components were stable. Signs of bone ingrowth into the stem and cup were evident on radiographs. The dog had a seven percent greater thigh muscle girth in the limb implanted with the hip prosthesis compared to the contralateral limb, and was very active with no lameness.

Influence of screw insertion order on compression generated by bone plates in a fracture model.

Present recommendations regarding order of screw insertion for compression plate osteosynthesis in veterinary training are variable. We hypothesized that placement of a neutrally positioned screw would reduce the magnitude of compression that could be generated by a subsequently placed compression screw. Canine tibial diaphyseal segments were fixed to a plate attached to a bone surrogate and load cell, and the compression generated by screw tightening was measured. Three different screw insertion order patterns were evaluated using both dynamic compression plate (DCP) and limited contact dynamic compression plate (LC-DCP) implants. In group CN, the first screw was placed in compression mode and the second in neutral mode; in group NC, the first screw was placed in neutral mode and the second in compression mode; in group LNC, the first screw was placed partially tightened in neutral mode and the second in compression mode followed by complete tightening of the neutral screw. Screw insertion order significantly influenced the amount of compression generated with both groups CN and LNC demonstrating significantly greater compression generation when compared with group NC (p <0.0001). Compression generated by group CN constructs was also significantly greater than group LNC (p = 0.0013). Evaluation of group CN data to assess the influence of plate and drill guide combinations on compressive force generated did not demonstrate a statistically significant difference. To maximize compression using a load screw in a bone plate, following securement of the opposite bone fragment to the plate, it should be placed before a neutral screw is placed.

Isometry of potential suture attachment sites for the cranial cruciate ligament deficient canine stifle.

For a suture that spans a joint to provide support without limiting range of motion, its attachment points on either side of the joint must remain the same distance from each other from full extension to full flexion. The effect of location of the tibial crest attachment for a fabello-tibial crest suture was studied in seven canine cadaveric stifles. The distance from a fabella marker to each of 11 tibial markers was determined from radiographs of each limb, as it progressed from 150 degrees to 130 degrees , 105 degrees , 90 degrees , 65 degrees and 45 degrees of flexion. The marker locations that were more proximal and cranial on the tibial crest had the least percent change in distance. The effect of anchoring the suture to the femur at a site other than the fabella was investigated using the same radiographs. Five marks were placed in a grid on the caudal portion of the femoral condyle and supracondylar region. The mean percent change in length from each femoral point to the five more proximal and cranial tibial markers was determined. The least change in length occurred for those femoral points located close to the origin of the cranial cruciate ligament. Locations more proximal or cranial resulted in large changes in length, particularly when matched with less ideal tibial locations. Although this study does not directly examine length changes in sutures, it demonstrates that there are some locations for the origin and insertion of an extracapsular suture that are associated with less length change than others, and also forms the basis for future investigations.

Amantadine in a multimodal analgesic regimen for alleviation of refractory osteoarthritis pain in dogs.

BACKGROUND: Nonsteroidal anti-inflammatory drugs (NSAIDs) do not always provide sufficient pain relief in dogs with osteoarthritis (OA). HYPOTHESIS: The use of amantadine in addition to NSAID therapy will provide improved pain relief when compared with the use of nonsteroidal analgesics alone in naturally occurring OA in dogs. ANIMALS: Thirty-one client-owned dogs with pelvic limb lameness despite the administration of an NSAID. METHODS: The study was randomized, blinded, and placebo controlled with parallel groups (days 21-42). On day 0, analgesic medications were discontinued. On day 7, all dogs received meloxicam for 5 weeks. On day 21, all dogs received amantadine (3-5 mg/kg once daily per os) or placebo for 21 days, in addition to receiving meloxicam. Assessments were performed before the study and on days 7, 21, and 42. Primary outcome measures were blinded owner assessments of activity using client-specific outcome measures (CSOM) on days 0, 7, 21, and 42. Data were analyzed by a mixed model approach. RESULTS: For CSOM activity, there was a significant time by treatment effect (P=.009). On the basis of the planned post hoc t-tests of postrandomization means, there was a significant difference between treatment groups on day 42 (P=.030), with the amantadine group being more active. CONCLUSIONS AND CLINICAL IMPORTANCE: In dogs with osteoarthritic pain refractory to an NSAID, physical activity is improved by the addition of amantadine. Amantadine might be a useful adjunct therapy for the clinical management of canine osteoarthritic pain.

Isometry of potential suture attachment sites for the medial aspect of the tibiotarsal joint.

The isometry of the bipartite medial collateral ligament of the tarsus and two methods of stabilization by prosthetic ligament were assessed by measuring the change in distance between the origin and the insertion through full range of joint motion of the ligament and prosthetic ligaments. The single suture technique was isometric when the distal site was located at the centre of the trochlea of the talus. This site can only be used when the medial malleolus, which overlies the talus, is missing or removed. Whilst some length changes occur with hock motion, the double suture technique may be advocated in instances where the medial malleolus is present.

An in vitro comparison of hollow ground and trocar points on threaded positive-profile external skeletal fixation pins in canine cadaveric bone.

OBJECTIVE: To compare the microstructural damage created in bone by pins with lathe-cut and rolled-on threads, and to determine the peak tip temperature and damage created by positive-profile external fixator pins with either hollow ground (HG) or trocar (T) tips during insertion. STUDY DESIGN: An acute, in vitro biomechanical evaluation. SAMPLE POPULATION: Twenty-seven canine tibiae. METHODS: Lathe-cut thread design with T point (LT-T), rolled-on thread design with T point (RT-T), and rolled-on thread design with HG point (RT-HG) pins were evaluated. Twenty pins of each type were inserted under constant drilling pressure into 12 canine tibiae (12 diaphyseal and 8 metaphyseal sites per pin type). Peak pin tip temperature, drilling energy, end-insertional pin torque, and pullout force were measured for each pin. For the histologic study, five pins of each type were inserted into cortical and cancellous sites in 15 additional tibiae. Entry and exit damage, and thread quality were assessed from 100 micron histologic sections by using computer-interfaced videomicroscopy. RESULTS: T-tipped pins reached higher tip temperature in both diaphyseal and metaphyseal bone compared with HG-tipped pins. RT-T pins had higher pullout strength (diaphyseal) and end-insertional torque compared with other combinations. No differences in drilling energy or insertional bone damage was found between the three pin types (P < .05). CONCLUSIONS: T-tipped pins mechanically outperformed HG-tipped pins. Pin tip and thread design did not significantly influence the degree of insertional bone damage. CLINICAL RELEVANCE: T-tipped pins may provide the best compromise between thermal damage and interface friction for maximizing performance of threaded external fixator pins.

Nitrous acid pretreatment of tendon xenografts cross-linked with glutaraldehyde and sterilized with gamma irradiation.

Collagenous xenografts made from kangaroo tail tendon cross-linked with glutaraldehyde have a potential application in the reconstruction of massive digital tendon deficits. However, a limitation to the clinical use of these xenografts has been the optimization of collagen cross-linking, and subsequent bio-incorporation and retention of mechanical properties following implantation. The purpose of this study was to evaluate the effect of nitrous acid on modulating the biologic and mechanical properties of tendon xenografts cross-linked with glutaraldehyde. Tendon xenografts were pretreated with 0.1 or 0.01 M nitrous acid solution, prior to cross-linking in 2% glutaraldehyde and sterilization by gamma irradiation. Xenografts were implanted intramuscularly in rabbits to examine biocompatability, and also used to repair ovine digital extensor tendon deficits to evaluate functional incorporation. Histologically, intramuscularly implanted nitrous acid pretreated xenografts in rabbits had a greater degree of diffuse cellular infiltration into interstitial splits in the graft than controls after 12 weeks. Xenografts implanted in an ovine extensor tendon deficit were evaluated after 26 and 52 weeks. Rate of failure of tenorrhaphies between host tendon and xenografts overall (15/21) was significantly greater (P < 0.05) than for autografts (1/21), suggesting that the holding power of sutures in xenografts was inferior to that obtained in autografts. Tensile failure stress of midsections of both nitrous acid pretreated and control xenografts was about 100 MPa prior to implantation (time zero). After 26 and 52 weeks, failure stress of both types of xenografts was significantly less than at time zero (P < 0.05). At 52 weeks, failure stress of nitrous acid pretreated xenografts (47.4 +/- 3.1 MPa) was significantly less than control xenografts (63.7 +/- 5.4 MPa); (P < 0.05). However, nitrous acid pretreated xenografts were similar to control xenografts in failure load (357 +/- 29 and 354 +/- 26 N, respectively), but they tended to have larger cross-sectional areas (7.6 +/- 0.5 versus 5.7 +/- 0.6 mm2, respectively) which were responsible for the lower calculated value for failure stress. Histologically, autografts maintained their normal tissue architecture and evoked a more limited cellular response in surrounding tissues than xenografts (P < 0.05). Both types of xenograft were surrounded by a thicker cuff of cellular response than autografts. However, compared to control xenografts, nitrous acid pretreated xenografts had more extensive fragmentation and splitting of collagen bundles, and more diffuse cellular and vascular infiltration into these interstitial splits, and these alterations were apparently contributing to the greater 'swelling' of these xenografts. It was concluded that pretreatment of tendon xenografts with nitrous acid modulated their biologic and material properties. Further studies are needed to elucidate the mechanism of these effects, and to determine if the protocol for tendon xenograft preparation could be optimized for improved clinical performance.

Assessment of the directional elastic moduli of ewe vertebral cancellous bone by vibrational testing.

The ovariectomized ewe is being used as an animal model for postmenopausal osteoporosis. Data on the mechanical properties of ewe vertebral cancellous bone is needed to assess its effectiveness as a model for vertebral osteoporosis. This study utilized traditional compression testing and a novel nondestructive vibrational testing method to assess the directional mechanical properties of ewe vertebral cancellous bone. Composition and density properties were also assessed. It was hypothesized that vibrational testing would have utility in that it would allow for the anisotropic stiffness of cancellous bone to be assessed nondestructively. The present study has found that ewe vertebral cancellous bone has similar physical and mechanical properties to humans. The vibrational testing method described was able to nondestructively provide a valid measure of stiffness that was correlated with stiffness estimates from traditional compression testing. Furthermore, the stiffness measure from the vibration test was found to be sensitive to the architecture of cancellous bone. These results suggest the promise of this testing method for the nondestructive mechanical assessment of skeletal tissue.

Interlocking nail treatment of diaphyseal long-bone fractures in dogs.

OBJECTIVE: To determine results of using interlocking nails (IN) for fixation of diaphyseal long bone fractures in dogs. DESIGN: Multi-center prospective clinical trial. ANIMALS: 134 dogs with diaphyseal fractures of the femur (n = 92), tibia (23), or humerus (19); 11 had previous unsuccessful treatments, and 103 had comminuted fractures of which 70 were classified as unstable. PROCEDURE: All fractures were stabilized with 6- or 8-mm-diameter IN with 3.5- or 4.5-mm screws, respectively. Cerclage wires and an autogenous bone graft were used at the surgeon's discretion. Participating surgeons provided information on age, sex, weight, and breed of the dog, details of the surgery, details of any intra- or postoperative complications, fracture healing time, and limb function. RESULTS: Eight dogs were lost to follow-up evaluation. In 105 of the remaining 126 dogs (83%), fractures healed without complications. For these 105 dogs, limb function was excellent (n = 90), good (12), fair (2), and poor (1). Complications developed for 21 dogs (17%); limb function after additional treatment was excellent (n = 10), good (2), fair (5), poor (1), or unreported (3). Interlocking nails broke in 9 dogs; breakage was attributed to fatigue failure because of use of too small an IN or because of insertion of the IN so that a screw hole was positioned at the fracture site. CLINICAL IMPLICATIONS: The high success rate and low complication rate suggest that IN can be used to stabilize diaphyseal fractures in dogs. Good technique is necessary for optimal results.

Biomechanical comparison of the trocar tip point and the hollow ground tip point for smooth external skeletal fixation pins.

OBJECTIVE: To compare the insertional characteristics of external fixator pins with hollow ground (HG), modified HG, and trocar (T) points. STUDY DESIGN: An acute, in vitro biomechanical evaluation. SAMPLE POPULATION: Thirteen radii from canine cadavers. METHODS: A total of 16 T-tipped and 16 HG-tipped pins were inserted into 8 canine radii. Ten pins of each modification of the HG tip (length of the cutting edge reduced by 0.127 mm and 0.254 mm, respectively) were inserted into another five radii. All pins were inserted with low-speed power drilling and 80 N drilling load. Differences between peak tip temperature, drilling energy, and pullout force were determined for each pin type at both diaphyseal and metaphyseal locations. RESULTS: HG-tipped pins showed a 40% lower tip temperature in diaphyseal bone, a 25% reduction in drilling energy in diaphyseal bone, and a reduction of pullout force in both diaphyseal (65%) and metaphyseal (50%) bone compared with T-tipped pins. HG 0.254-mm pins generated higher tip temperatures and had greater pullout than HG pins in diaphyseal bone. CONCLUSIONS: The HG tip was a more efficient design; however, the reduction in pullout force suggests that, because a better hole was drilled, radial preload is reduced. Reduction of the cutting edge by 0.254 mm increased the pullout force but also increased the temperatures. CLINICAL RELEVANCE: Thermal and microstructural damage are reduced by the HG tip, but pin-bone interface stability is also compromised. The use of a tip with 0.254 mm reduction in the cutting edge may optimize the biological and mechanical factors at the pin-bone interface.

Holding power of different pin designs and pin insertion methods in avian cortical bone.

OBJECTIVE: To measure pullout strength of four pin types in avian humeri and tibiotarsi bones and to compare slow-speed power and hand insertion methods. STUDY DESIGN: Axial pin extraction was measured in vitro in avian bones. ANIMAL POPULATION: Four cadaver red-tailed hawks and 12 live red-tailed hawks. METHODS: The pullout strength of four fixator pin designs was measured: smooth, negative profile threaded pins engaging one or two cortices and positive profile threaded pins. Part 1: Pins were placed in humeri and tibiotarsi after soft tissue removal. Part 2: Pins were placed in tibiotarsi in anesthetized hawks using slow-speed power or hand insertion. RESULTS: All threaded pins, regardless of pin design, had greater pullout strength than smooth pins in all parts of the study (P < .0001). The cortices of tibiotarsi were thicker than the cortices of humeri (P < .0001). There were few differences in pin pullout strengths between threaded pin types within or between bone groups. There were no differences between the pullout strength of pins placed by slow-speed power or by hand. CONCLUSIONS: There is little advantage of one threaded pin type over another in avian humeri and tibiotarsi using currently available pin designs. There were few differences in pin pullout strengths between humeri and tibiotarsi bones. It is possible that the case of hand insertion in thin cortices minimizes the potential for wobbling and therefore minimizes the difference between slow-speed drill and hand insertion methods. CLINICAL RELEVANCE: Threaded pins have superior bone holding strength in avian cortices and may be beneficial for use with external fixation devices in birds.

Hinged Ilizarov external fixation for correction of antebrachial deformities.

OBJECTIVE: To evaluate hinged circular external fixation for correction of antebrachial deformities in dogs. STUDY DESIGN: Uncontrolled clinical trial. ANIMAL POPULATION: Seven client-owned dogs. METHODS: Six dogs had one radius corrected and one dog had both radii corrected. Preoperative planning included measurement of the craniocaudal and mediolateral angular deformities, rotational deformity, length deficit, origin of deformity, graphical or mathematical determination of the amplitude and direction of the actual limb deformity, and frame assembly. RESULTS: Preoperatively, function and cosmesis were assessed to be fair to poor in all dogs. Deformity correction started 48 to 60 hours postoperatively and ranged from 0.46 mm to 1.36 mm twice daily. Hospitalization time ranged from 4 to 6 days. Corrections were mostly made by the owners, at home. Lengthening and angular correction ranged from 3 to 38 mm and 18 degrees to 48 degrees. Mean residual deformities were 2.7% of radial length and 2.7 degrees. The time duration with the circular external fixators in place ranged from 29 to 71 days. Two additional surgeries were necessary in one dog because of wire breakage. Mean follow-up was 40 months. Long-term function and cosmesis were good to excellent in all dogs. CONCLUSION: Although complications were present in six of seven dogs, the outcome of hinged Ilizarov external fixation was successful in all dogs treated for deformities of the antebrachium. CLINICAL RELEVANCE: Despite complex preoperative planning, the placement of hinged circular external fixators is straightforward, and allows precise correction of complex antebrachial deformities with minimal tissue trauma.

Axial vibration of threaded external fixation pins: detection of pin loosening.

The hypothesis of this study was that a nondestructive vibrational method could detect bone lysis at the external fixation pin-bone interface prior to current clinical and radiographic methods. In vitro models were used to simulate changes observed during pin loosening in vivo. Fixation pin axial natural frequency decreased with decreasing tensile modulus of the material into which it was implanted. In a live animal study the right tibia of 12 dogs was fractured and stabilized with a four-pin unilateral external fixation frame. The axial natural frequency of each pin was measured and radiographs were taken at 0, 2, 4, 6, 8, and 10 weeks after surgery. The natural frequency did not change when the first radiographic changes around the interface were observed. Pins were palpably stable at this point. As loosening progressed, the natural frequency did decrease. Frequency and quasistatic tests of dissected pin-bone structures revealed a good correlation between natural frequency and pin-bone interface stiffness. In addition, the measurement of natural frequency was more sensitive to bone structure changes at the pin-bone interface than low-load quasi-static stiffness. Therefore, a nondestructive vibration technique could be used instead of low-load quasistatic tests for assessing the pin-bone interface ex. vivo.

Epoxy putty for free-form external skeletal fixators.

OBJECTIVE: To evaluate the suitability of epoxy putty for use as a connecting beam material in a free-form external skeletal fixator. DESIGN: Mechanical evaluation of beams and the pin-material interface of commonly used methacrylates and the proposed epoxy putty. PROCEDURE: The apparent modulus, bending strength, and toughness of 10 beams of three methacrylates (Technovit, APEF System, Bone Cement) and three epoxy putties (Oatey Epoxy Putty, All-Metals PowerPoxy, and Plumber's PowerPoxy) were determined in three-point bending. The shear strength of smooth and roughened-shaft pins embedded in the three methacrylates and the Oatey Epoxy Putty was determined by pull-out testing. RESULTS: The epoxy putties had similar strength, greater apparent modulus, and reduced toughness when compared with the methacrylates. The shear strength of the smooth pin interface with the Oatey Epoxy putty was greater than that with the methacrylates. The interface with roughened pins was much stronger than that with smooth pins for all materials tested. CLINICAL RELEVANCE: Epoxy putty is a suitable material for free-form external fixators. It is easy to handle, inexpensive, and has suitable setting times and mechanical properties.

Mechanical characteristics and comparisons of cerclage wires: introduction of the double-wrap and loop/twist tying methods.

OBJECTIVE: Evaluate the mechanical properties of twist, loop, double loop, double-wrap and loop/twist cerclage. METHODS: The initial tension generated by 18 cerclage of each type was determined using a materials testing machine after tying around a testing jig. Six wires from each type were distracted and the initial stiffness and yield load were determined. Yield behavior was further investigated in six wires of each type by determining the load required to reduce cerclage tension below 30 Newton (N) following and incremental (50 N) stepwise load and unload regimen. The amount of collapse of the simulated bone fragments that resulted in the reduction of initial tension to 30 N was measured for the final six wires of each group. Data were analyzed by analysis of variance and a multiple comparison test. RESULTS: Twist type cerclage generated less tension than loop-type cerclage. The yield load of these two types was similar. Double-loop and double-wrap cerclage generated superior tension and resisted a greater load before loosening. Loop/twist cerclage had an intermediate initial tension but had the greatest resistance to loading. In the collapse test, the greater the initial tension, the more collapse could occur before the wire was loose. For all types of cerclage wire fixation, a reduction of diameter of the testing jig of more than 1% caused loosening. CLINICAL RELEVANCE: Double-loop and double-wrap cerclage provide greater compression of fragments and resist loads associated with weight-bearing better than the twist and loop methods. Loop/twist cerclage may have advantages because of their superior resistance to loading. All cerclage will loosen if fracture fragments collapse.

In vitro biomechanical and histological assessment of pilot hole diameter for positive-profile external skeletal fixation pins in canine tibiae.

This study was conducted to evaluate the effect of pilot hole (PH) diameter (0, 1.5, 2.0, 2.7, 3.1, 3.3, 3.5, and 3.7 mm) on the biomechanical and microstructural performance of positive-profile threaded external skeletal fixation pins (3.18 mm inner diameter, 3.97 mm outer diameter) using cadaveric canine tibiae. Eight pins per pilot hole diameter (four pins per bone) were used to assess differences in end-insertional torque and pin pull-out strength. Histological evaluation of eight bicortical pin tracts per pilot hole diameter was accomplished using computer-interfaced videomicroscopy on specimens processed using a bulk-staining technique. Compared with no predrill, use of 2.7 mm PH increased end-insertional torque and pull-out strength by 25% and 13.5%, respectively. No significant differences were observed in biomechanical variables for the PH diameter range of 2.0 to 3.1 mm. Compared with no predrill, use of a 3.1 mm PH increased thread area by 18%. Microfracturing around the threads decreased as PH diameter increased. Damage to the interface at the entry and exit sites of both near and far cortices also decreased as PH diameter increased. It was concluded that predrilling a PH whose diameter approximates, but does not exceed the inner diameter of the positive profile pin will not only improve initial pin stability compared with no predrilling, but it will also reduce microstructural damage that may lead to excessive bone resorption and premature pin loosening.